Son of a gun!!! Thank you so much! I spent HOURS changing every setting except this one and actually came to the conclusion that it must be something to do with my ISP's modem or DNS or something.
The rule is the "associated filter rule" OPNsense automatically creates (interfaces are WAN and LAN) and it triggers as a "pass" just fine when I send a request. (I'm attaching another screenshot from the live log below.)
You don't happen to have a clue WHY this rule breaks everything?